The current method of measuring SpO2 is mainly using the probes with reflective optical principle. If users’ fingers wear nail polish, it would make pulse oximeter unable to measure the accurate data in actual usages. Furthermore, the measuring by probes also needs stable posture. It greatly limits the convenience of usage. ZoeTek has already developed the related algorithm for SpO2 measurement and has embedded it in smart devices.

Principle of SpO2 Measurement

Figure 5. Absorbances of oxyhemoglobin and deoxygenated hemoglobin in different wavelengths.

The measurement of SpO2 is based on the difference of absorbances with different wavelengths between oxyhemoglobin and deoxygenated hemoglobin. When utilizing two light with different wavelengths to irradiate fingers, we receive the reflective light by photodetector. The signals from the photodetector receiver would include the composition of AC signal and DC signal.